1. Field of the Invention
The present invention relates to a brake system of a vehicle. More particularly, it relates to an antiskid control device to prevent wheels of the vehicle from locking when the brake system is operated, so that drivability of the vehicle is maintained.
2. Description of the Related Art
In conventional brake system of a vehicle, a master cylinder, a reservoir, and wheel cylinders are connected through a piping (line) system so that, when a brake pedal is operated, oil pressure generated in the master cylinder is transmitted to the wheel cylinder, and when the brake pedal is released, the oil in the master cylinder is released to the reservoir and thus the pressure in the wheel cylinder is reduced. An antiskid control device is provided in the brake system, and a valve disposed in a line between the master cylinder and the wheel cylinder is controlled according to a state of a wheel, so that oil pressure in the wheel cylinder is reduced when the wheel locks.
Such an antiskid control device is disclosed, for example, in Japanese Examined Patent Publication Nos. 49-28307 and 49-32494.
The above conventional construction, in which a usual braking operation and antiskid operation are carried out by one line system, has the following problems. If the line system and the control valve are constructed so as to supply enough pressurized oil to the wheel cylinders during a usual braking operation, the flow rate of the pressurized oil supplied to the wheel cylinders during antiskid control is too high to ensure control stability. Conversely, if the line system and the control valve are constructed so as to supply a relatively small quantity of pressurized oil to the wheel cylinders for the antiskid control, the quantity of pressurized oil supplied to the wheel cylinder during a usual braking operation is too small to obtain a sufficient braking effect.